Bioresorbable embolization microspheres

ABSTRACT

The present disclosure is generally directed to an embolic material which, in some embodiments, may be in the form of a microsphere or a plurality of microspheres. The embolic material generally comprises carboxymethyl chitosan (CCN) crosslinked with carboxymethyl cellulose (CMC). In some embodiments, the embolic material may further comprise a therapeutic agent, such as doxorubicin.

This application is a continuation of U.S. application Ser. No.16/206,199, entitled “BIORESORBABLE EMBOLIZATION MICROSPHERES,” filedNov. 30, 2018, which is a is a continuation of U.S. application Ser. No.14/098,443, entitled “BIORESORBABLE EMBOLIZATION MICROSPHERES,” filedDec. 5, 2013, which is a continuation of U.S. application Ser. No.12/899,238, entitled “BIORESORBABLE EMBOLIZATION MICROSPHERES,” filedOct. 6, 2010, which claims the benefit of U.S. Provisional ApplicationNo. 61/249,194, entitled, “EMBOLIZATION MICROSPHERES,” filed on Oct. 6,2009. The entire contents of each of U.S. application Ser. Nos.16/206,199, 14/098,443, and 12/899,238, and U.S. Provisional ApplicationNo. 61/249,194 are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to embolic materials.

BACKGROUND

Transcatheter arterial embolization (TAE) has been widely accepted forits efficacy in treating various diseases including tumors, vascularlesions, and hemorrhages. For a safe and effective treatment, theselection of an appropriate embolic material is important.

SUMMARY

In general, the disclosure is directed to an embolic material comprisingcarboxymethyl chitosan (CCN) crosslinked with carboxymethyl cellulose(CMC). The embolic material may be formed into microspheres with adiameter between about 50 micrometers (μm) and about 2200 μm. CCN andCMC each are biodegradable and biocompatible. In preparing the embolicmaterial, CCN may be crosslinked by partially oxidized CMC, without useof a small molecule crosslinking agent. Because of this, the embolicmaterial is expected to be biodegradable and biocompatible.Additionally, because the embolic material comprises a three-dimensionalnetwork of CCN crosslinked by CMC, the mechanical properties, such as,for example, the compressibility of the embolic microspheres, may besufficient to permit introduction of the microspheres into an artery ofa patient through a syringe, catheter, or the like.

In some embodiments, the embolic microspheres may additionally comprisea therapeutic agent, such as an anti-cancer agent. One example of atherapeutic agent which may be loaded into the embolic microspheres isdoxorubicin.

In one aspect, the disclosure is directed to an embolic materialcomprising a microsphere having a diameter between about 50 μm and about2200 μm, where the microsphere comprises carboxymethyl chitosancrosslinked with carboxymethyl cellulose.

In another aspect, the disclosure is directed to an embolizationsuspension comprising a solvent and a plurality of microspheressuspended in the solvent. According to this aspect of the disclosure, atleast one of the plurality of microspheres comprises a diameter betweenabout 50 μm and about 2200 μm, and at least one of the plurality ofmicrospheres comprises carboxymethyl chitosan crosslinked withcarboxymethyl cellulose.

In a further aspect, the disclosure is directed to a kit comprising aplurality of microspheres, where at least one of the plurality ofmicrospheres comprises a diameter between about 50 μm and about 2200 μm,and where at least one of the plurality of microspheres comprisescarboxymethyl chitosan crosslinked with carboxymethyl cellulose.According to this aspect of the disclosure, the kit further comprises asyringe or vial in which the plurality of microspheres is disposed.

In an additional aspect, the disclosure is directed to a method offorming an embolic microsphere. The method comprises at least partiallyoxidizing carboxymethyl cellulose (CMC) to form partially oxidized CMC;forming an emulsion of partially oxidized CMC, carboxymethyl chitosan(CCN), water, and an oil; and crosslinking the CCN with the CMC to formthe embolic microsphere.

In a further aspect, the disclosure is directed to a method comprisinginjecting an embolic microsphere comprising carboxymethyl chitosancrosslinked with carboxymethyl cellulose in a blood vessel of a patientto occlude an artery of the patient.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages of the disclosure will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow diagram of an example technique for producing embolicmicrospheres comprising carboxymethyl chitosan crosslinked withcarboxymethyl cellulose.

FIGS. 2A and 2B are a photograph and a light microscopy image,respectively, of microspheres in accordance with one aspect of thedisclosure.

FIG. 3 is an example of a scanning electron microscopy image of anexterior of a microsphere formed in accordance with aspects of thisdisclosure.

FIGS. 4A and 4B are examples of SEM images of the cross-section of ahydrogel prepared with CCN crosslinked with CMC.

FIGS. 5A-5F are light microscopy images illustrating loading of a dyeinto microspheres comprising CCN crosslinked with CMC.

FIGS. 6A-6C illustrate examples of microspheres according to an aspectof the disclosure after being loaded with various dyes.

FIGS. 7A-7D are light microscopy images illustrating an example ofloading doxorubicin into microspheres comprising CCN crosslinked withCMC.

FIG. 8 is an image illustrating an example of microspheres comprisingCCN crosslinked with CMC loaded with doxorubicin suspended in a solventmixture.

FIG. 9 is a scatter diagram illustrating examples of dynamics of loadingdoxorubicin into microspheres comprising CCN crosslinked with CMC ofvarious sizes.

FIG. 10 is a scatter diagram illustrating examples of dynamics ofloading doxorubicin into microspheres of various sizes.

FIG. 11 is a scatter diagram that illustrates examples of changes indiameter for microspheres of different initial diameters during loadingof doxorubicin.

FIG. 12 is an example fluorescence microscopy image of a microsphereloaded with doxorubicin.

FIG. 13 is an example image illustrating fluorescence intensity as afunction of distance for a single doxorubicin-loaded microsphere.

FIG. 14 is a scatter diagram illustrating examples of a percentage ofdoxorubicin released as a function to time for each of a plurality ofsamples of microspheres having different characteristics in accordancewith the disclosure.

FIG. 15 is a scatter diagram illustrating examples of an amount ofdoxorubicin released as a function to time for each of a plurality ofsamples of microspheres having different characteristics in accordancewith the disclosure.

FIG. 16 is a scatter diagram illustrating examples of an amount ofdoxorubicin released in a saline medium as a function to time for eachof a plurality of samples of microspheres having differentcharacteristics in accordance with the disclosure.

FIG. 17 is a scatter diagram illustrating examples of an amount ofdoxorubicin released in a saline medium as a function to time for eachof a plurality of samples of microspheres having differentcharacteristics in accordance with the disclosure.

FIG. 18 is a scatter diagram illustrating examples of an amount ofdoxorubicin released in a saline medium as a function to time for eachof a plurality of samples of microspheres having differentcharacteristics in accordance with the disclosure.

FIG. 19 is a line diagram that illustrates an example comparison ofdoxorubicin release rate between microspheres of two different diameterranges.

FIG. 20 is a line diagram that illustrates examples of release ofdoxorubicin from microspheres in different media.

FIG. 21 is a line diagram that illustrates an example of the effect thedegree of oxidation of the CMC may have on the release rate ofdoxorubicin from microspheres that are formed of CCN crosslinked withCMC.

FIG. 22 is a line diagram that illustrates an example of the effect ofthe medium on the release of doxorubicin from the microspheres.

FIG. 23 is a line diagram that illustrates an example comparison betweenrelease rates of doxorubicin from microspheres according to an aspectthe current disclosure and DC Beads™.

FIG. 24 is an example of a plot of compression force versus distance fora single microsphere having a diameter of about 715 μm.

FIGS. 25A-25C are light microscopy images illustrating an example of thecompressibility of a microsphere comprising CCN crosslinked with CMC(dyed with Evan's blue) as the microsphere passes through a polyethylenetube.

FIGS. 26A-26C are light microscopy images that illustrate anotherexample of the compressibility of a microsphere comprising CCNcrosslinked with CMC (dyed with Evan's blue) as the microsphere passesthrough a polyethylene tube.

FIGS. 27A and 27B illustrate an example of the resiliency of amicrosphere comprising CCN crosslinked with CMC (dyed with Evan's blue).

FIG. 28 is a light microscopy image of an example of microspherescomprising CCN crosslinked with CMC and having diameters between about500 μm and about 700 μm after being injected through a catheter with aninternal diameter of about 667 μm (2 French).

FIGS. 29A and 29B are light microscopy images of an example ofmicrospheres comprising CCN crosslinked with CMC and having diametersbetween about 800 μm and about 1000 μm after being injected through acatheter with an internal diameter of about 1 mm (3 French).

FIGS. 30A and 30B are light microscopy images of an example ofmicrospheres comprising CCN crosslinked with CMC and loaded withdoxorubicin while passing through a catheter and after passing throughthe catheter.

FIGS. 31A and 31B are light microscopy images of an example ofmicrospheres comprising CCN crosslinked with CMC and loaded withdoxorubicin while passing through a polyethylene tube.

FIGS. 32A and 32B are images illustrating microspheres comprising CCNcrosslinked with CMC suspended in two 4:6 contrast/saline mixtures.

FIG. 33 is a light microscopy image of an example of a plurality ofmicrospheres comprising CCN crosslinked with CMC after being stored fortwo months in water.

FIGS. 34A-34E are light microscopy images that illustrate an example ofa plurality of microspheres comprising CCN crosslinked with CMCdegrading in the presence of lysozyme.

FIGS. 35A-35C are light microscopy images that illustrate an example ofa plurality of microspheres loaded with doxorubicin degrading in thepresence of lysozyme.

FIGS. 36A and 36B are light microscopy images illustrating an example ofhuman dermal fibroblasts cultured with microspheres comprising CCNcrosslinked with CMC according to an aspect of the disclosure.

FIGS. 37A and 37B are light microscopy images of an example controlincluding cultured human fibroblast and an example of a sample includinghuman fibroblast cultured with microspheres comprising CCN crosslinkedwith CMC according to an aspect of the disclosure.

FIG. 38A-38C are light microscopy images illustrating an example ofhuman dermal fibroblasts stained with crystal violet.

FIG. 39A-39C are light microscopy images illustrating an example of asample including human dermal fibroblast cultured with microspherescomprising CCN crosslinked with CMC according to an aspect of thedisclosure.

FIG. 40 is a bar graph that illustrates an example of absorbance at awavelength of about 490 nm of medium cultured with human dermalfibroblasts after being treated with MTS

FIG. 41 is a bar graph that illustrates an example of the arterialdistribution of the microspheres after embolization of three pairs ofrabbit kidneys with microspheres having diameters between about 100 μmand about 300 μm.

FIG. 42 is bar diagram that illustrates an example comparison betweenEmbospheres® and microspheres formed of CCN crosslinked with CMC of themean diameter of the vessel occluded during an embolization procedure.

FIG. 43 is a bar diagram that illustrates an example determination ofthe mean diameter of the microspheres formed of CCN crosslinked with CMCthat were used in the embolization procedure that generated the resultsshown in FIG. 43 .

FIGS. 44 and 45 are example histology sections of kidney tissue showingarcuate artery in a kidney of a rabbit occluded with an embolicmicrosphere according to aspects of the disclosure.

DETAILED DESCRIPTION

The present disclosure is generally directed to an embolic materialwhich, in some embodiments, may be in the form of a microsphere or aplurality of microspheres. The embolic material generally comprisescarboxymethyl chitosan (CCN) crosslinked with carboxymethyl cellulose(CMC).

Temporary embolization may be accomplished by a material that isspherical, biocompatible, bioresorbable, and compressible. However,these properties are not easily achieved in a single embolicmicrosphere. For example, crosslinking of polymers may be accomplishedby using a small molecule crosslinking agent, such as glutaraldehyde.While use of the small molecule crosslinking agent facilitates thedesired crosslinking reaction, if the crosslinked polymer isbiodegradable and degrades in a body of a patient, some small-moleculecrosslinking agents may be toxic or have other adverse effects on cellsor tissue in the body of the patient.

In accordance with aspects of this disclosure, CCN and CMC may becrosslinked without use of a small molecule crosslinking agent to formembolic microspheres that are substantially free of small moleculecrosslinking agent. In fact, in some embodiments, the crosslinkingreaction between CMC and CCN may be carried out without a small moleculecrosslinking agent and at relatively low temperatures (e.g., about 50°C.) in a water and oil emulsion. CCN is substantially non-toxic andbiodegradable. Chitosan breaks down in the body to glucosamine, whichcan be substantially completely absorbed by a patient's body. Similarly,CMC is substantially non-toxic and biodegradable. Thus a crosslinkedpolymer formed by CCN and CMC is expected to the substantially non-toxic(i.e., biocompatible) and biodegradable (or bioresorbable).Additionally, because the crosslinked CCN and CMC microsphere is formedfrom two polymers, the mechanical properties, such as compressibility,of the crosslinked molecule are expected to be sufficient for injectionof the crosslinked molecule through a syringe or catheter.

Because the crosslinking reaction between CCN and CMC may be performedat a relatively low temperature, the crosslinking reaction may berelatively slow in some examples. For example, the crosslinking reactionmay be carried out over night (e.g., over at least about 12 hours). Sucha reaction may result in roughly spherical crosslinked particles(microspheres). In some examples, an average diameter of themicrospheres may be between about 50 μm and about 2200 μm, depending onreaction conditions (e.g., stirring speed, initial concentrations ofreactants, time, temperature, or the like).

In some embodiments, the microspheres comprising CCN and CMC may beformed according to the technique illustrated in FIG. 1 . Initially, CMCis at least partially oxidized to form partially oxidized CMC (12). Onereaction that at least partially oxidizes CMC is illustrated in Reaction1:

In Reaction 1, a single CMC monomer (repeating unit), which is part of achain comprising n repeating units, is reacted with NaIO₄ (sodiumperiodate) at about 25° C. to oxidize the C—C bond between carbon atomsbonded to hydroxyl groups to form carbonyl (more particularly aldehyde)groups. Reaction 1 shows only a single repeating unit of the CMCpolymer. In some embodiments, not all repeating units within the CMCpolymer may be oxidized. For example, some repeating units may not beoxidized at all, and may still include two hydroxyl groups afterReaction 1 is performed. Other monomers may be oxidized, and may includetwo carbonyl groups, as illustrated in Reaction 1. The CMC may include aweight average molecular weight of between about 50,000 daltons (Da;equivalent to grams per mole (g/mol)) and about 800,000 Da. In someembodiments, a weight average molecular weight of the CMC may be about700,000 g/mol.

The degree of oxidation of the CMC may be affected by, for example, themolar ratio of NaIO₄ to CMC repeating units. In some embodiments, themolar ratio of NaIO₄ molecules to CMC repeating units may be betweenabout 0.1:1 and about 0.5:1 (NaIO₄:CMC). Particular examples of molarratios of NaIO₄ molecules to CMC repeating units include about 0.1:1,about 0.25:1, and about 0.5:1. An increased molar ratio of NaIO₄molecules to CMC repeating units may result in greater oxidation of theCMC, which in turn may lead to greater crosslinking density when CMC isreacted with CCN to form the embolic microspheres. Conversely, adecreased molar ratio of NaIO₄ molecules to CMC repeating units mayresult in lesser oxidation of the CMC, which in turn may lead to lowercrosslinking density when CMC is reacted with CCN to form the embolicmicrospheres. In some examples, the crosslinking density may beapproximately proportional to the degree of oxidation of the CMC. Insome embodiments, a greater crosslinking density may lead to greatermechanical strength (e.g., fracture strain).

CCN may then be prepared by reacting chitosan to attach —CH₂COO⁻ groupsin place of one of the hydrogen atoms in an amine group or a hydroxylgroup, as illustrated in Reaction 2 (14).

In the product of Reaction 2, each R is independently either H or—CH₂COO⁻. Similar to oxidation of CMC shown in Reaction 1, the extent ofthe addition of the —CH₂COO⁻ may affect the crosslink density when theCCN is reacted with the partially oxidized CMC to form the embolicmicrospheres. In some embodiments, the ratio of x:y may be about 3:1(i.e., monomers of “x” form about 75% of the chitosan and monomers of“y” form about 25% of the chitosan). In some embodiments, the chitosanstarting material may have a molecular weight between about 190,000g/mol and about 375,000 g/mol. In some examples, Reaction 2 may beperformed by stirring the reaction mixture at 500 rpm for about 24 hoursat about 25° C., followed by stirring the reaction mixture at 500 rpmfor about 4 hours at about 50° C.

Once the partially oxidized CMC and the CCN have been prepared, each ismixed in a respective amount of a solvent, such as water (16), (18). Forexample, 0.1 milligram (mg) of partially oxidized CMC may be mixed in 5milliliter (mL) of water to form a first 2% weight/volume (w/v)solution. Similarly, 0.1 mg of CCN may be mixed in 5 mL of water to forma second 2% w/v solution. Of course, solvents other than water may beused, and solutions having other concentrations of partially oxidizedCMC or CCN, respectively, may be utilized. For example, saline orphosphate-buffered saline (PBS) may be utilized as alternative solvents.The solvent used in the partially oxidized CMC solution may be the sameas or different than the solvent used in the CCN solution. The solutionsmay have concentrations of partially oxidized CMC or CCN between about0.5% w/v and about 3% w/v. The concentration of the partially oxidizedCMC solution may be the same as or different from the concentration ofthe CCN solution.

The first and second solutions may then be added to another solvent toform an emulsion (20). In an example in which water is utilized as thesolvent for the partially oxidized CMC and CCN, the other solvent may bean oil, such as, for example, mineral oil. In some embodiments, theother solvent may include mixed therein a surfactant. One example of asuitable surfactant includes sorbitan monooleate, available under thetradename 56760 or Span® 80 from Sigma-Aldrich, St. Louis, Mo. In oneembodiment, 0.5 mL of sorbitan monooleate may be mixed in 50 mL ofmineral oil, which is then mixed with the 5 mL 2% w/v solution ofpartially oxidized CMC and the 5 mL 2% w/v solution of CCN.

The emulsion is then left for at least about 12 hours (e.g., at leastovernight) to allow the partially oxidized CMC and CCN to react (22) ina modified emulsion-crosslinking reaction. In particular, an amino groupon the CCN may react with an aldehyde group on the partially oxidizedCMC to form a Schiff base (i.e., an N═C double bond) and crosslink theCMC and the CCN. One such crosslinking reaction is shown below inReaction 3.

As discussed above, the crosslinking reaction of the CMC and CCN mayproceed without use of a small-molecule crosslinking agent, such asglutaraldehyde. This may be advantageous, because in some embodiments, asmall-molecule crosslinking agent may be toxic to a patient in which theembolic microspheres are used. In this way, the microspheres formed fromCCN crosslinked with CMC may be substantially free of any small-moleculecrosslinking agent.

In some examples, the crosslinking reaction between CMC and CCN mayproceed under relatively benign conditions. For example, thecrosslinking reaction may be carried out at ambient pressures andambient temperatures (e.g., room temperature). In some embodiments, thereaction may be carried out at a temperature above ambient, such as, forexample, 50° C. Exemplary ranges of temperatures in which thecrosslinking reaction may be performed include between about 20° C. andabout 70° C., and at about 50° C. In some embodiments, a lower reactiontemperature may necessitate a longer reaction time to result insubstantially similar diameter microspheres, or may result in smallermicrospheres after a similar amount of time.

One advantage of performing the reaction at a temperature above roomtemperature may be the removal of water from the reaction mixture duringthe course of the reaction. For example, performing the crosslinkingreaction at a temperature of about 50° C. may result in evaporation ofwater as the crosslinking reaction proceeds.

An extent of crosslinking between molecules of CMC and CCN may affectmechanical properties of the resulting microsphere. For example, agreater crosslinking density generally may provide greater mechanicalstrength (e.g., fracture strain), while a lower crosslinking density mayprovide lower mechanical strength (e.g., fracture strain). In someembodiments, the crosslinking density may be adjustable to provide afracture strain of between about 70% and about 90%, as described belowwith respect to FIG. 24 . The crosslinking density may also affect thedegradation rate of the microsphere. For example, a greater crosslinkingdensity may lead to a longer degradation time, while a lowercrosslinking density may lead to a shorter degradation time. In someexamples, the crosslink bonds may degrade through hydrolyzing of the C═Ndouble bond.

As described above, the crosslinking reaction between CMC and CCN is amodified emulsion-crosslinking reaction. In some examples, anemulsion-crosslinking reaction may be rate-limited by transport of theCMC and CCN molecules, and may play a role in the reaction product (thecrosslinked CMC and CCN) being microspheres.

The size of the microspheres may be affected by reaction conditions,such as, for example, a stirring speed, a reaction temperature, aconcentration of the CMC and CCN molecules in the reaction emulsion, anamount of mixing of the emulsion, or a concentration of the surfactantin the emulsion. For example, increasing the concentration of each ofthe CMC and CCN solutions from 1.5% w/v to 2% w/v while keeping theoxidation degree of CMC at about 25% (about 25 oxidized repeating unitsper 100 total repeating units), the stirring speed at 600 revolutionsper minute (rpm), the temperature at about 50° C., the reaction time atabout 12 hours, and the amount of Span 80 at about 0.3 mL/50 mL mineraloil, the average diameter of the microspheres may increase from about600 μm to about 1100 μm. As another example, increasing the oxidationdegree of CMC from about 10% to about 25% while keeping theconcentration of each of the CMC and CCN solutions at about 1.5% w/v,the stirring speed at 600 rpm, the temperature at about 50° C., thereaction time at about 12 hours, and the amount of Span 80 at about 0.3mL/50 mL mineral oil, the average diameter of the microspheres mayincrease from about 510 μm to about 600 μm.

In some embodiments, the reaction conditions may be selected to resultin microspheres with a mean or median diameter between about 50 μm andabout 2200 μm. In some embodiments, the reaction conditions may beselected to result in microspheres with a mean or median diameter ofless than about 2000 μm, microspheres with a mean or median diameter ofbetween about 100 μm and about 1200 μm, microspheres with a mean ormedian diameter of between about 100 μm and about 300 μm, microsphereswith a mean or median diameter of between about 300 μm and about 500 μm,microspheres with a mean or median diameter of between about 500 μm andabout 700 μm, microspheres with a mean or median diameter of betweenabout 700 μm and about 900 μm, microspheres with a mean or mediandiameter of between about 900 μm and about 1200 μm, or microspheres witha mean or median diameter of between about 1600 μm and about 2000 μm.

In some examples, microspheres with different mean or median diametersmay be used for different applications. For example, in someimplementations, microspheres with a mean or median diameter betweenabout 100 μm and about 300 μm may be loaded with a therapeutic agent,such as a chemotherapeutic agent as described further below, and used todeliver the therapeutic agent to a therapy site, while also embolizingblood vessels with a diameter similar to the mean or median diameter ofthe microspheres. In some embodiments, microspheres with a mean ormedian diameter between about 300 μm and about 500 μm may be usedsimilarly, and loaded with a therapeutic agent. In some embodiments,microspheres with a larger mean or median diameter may be used asembolization materials, and may not be loaded with a therapeutic agent.

Once the reaction has proceeded for a desired amount of time to producemicrospheres with a desired mean or median diameter, the water in theemulsion may be substantially fully removed, if the water has notalready been evaporated during the crosslinking reaction. Themicrospheres may then be precipitated by a solvent, such as isopropanol.The oil phase may then be removed, such as by decanting orcentrifugation, and the microspheres may be washed (24). For example,the microspheres may be washed with hexane and acetone. Finally, themicrospheres may be dried (26) in air or under a vacuum.

In some embodiments, the crosslinking reaction may produce a pluralityof microspheres with diameters distributed about a mean or median. Insome cases, it may be advantageous to isolate microspheres withdiameters within a smaller range or microspheres with substantially asingle diameter. In some embodiments, the microspheres may be separatedaccording to diameter by wet sieving in normal saline through a sieve orsieves with predetermined mesh size(s).

The microspheres may be packaged for distribution in various ways. Forexample, the microspheres may be distributed as part of a kit. In someembodiments, the kit may include the microspheres disposed in a syringeor a vial. The kit may optionally include a catheter, a guide wire,and/or a container of solution in which the microspheres are to besuspended. The catheter may be used to inject the microspheres into ablood vessel of a patient. The guide wire may be used to position thecatheter within the blood vessel.

In some embodiments, the kit may be an emergency trauma kit for acuteembolization in massive bleeding trauma. Such a kit may include, forexample, a syringe or vial and a plurality of microspheres disposed inthe syringe or vial. In some embodiments, the microspheres may comprisean average diameter of between about 1600 μm and about 2000 μm. In otherembodiments, the microspheres may comprise a different average diameter,such as an average diameter within a range listed in other portions ofthis application. In some embodiments, the kit may further include acatheter, a guide wire for positioning the catheter within a bloodvessel, such as an artery, of the patient, and/or a container ofsolution in which the microspheres are to be suspended. Prior toinjection of the microspheres, the solution may be aspirated into thesyringe to form a suspension of the microspheres in the solution.

The microspheres may be used to embolize arteries to treat variousconditions, including, for example, an arteriovenous malformation, acerebral aneurysm, gastrointestinal bleeding, an epistaxis, primarypost-partum hemorrhage, or the like.

FIGS. 2A and 2B are a photograph and a light microscopy image ofmicrospheres in accordance with one aspect of the disclosure. FIG. 2Aillustrates that microspheres in accordance with the disclosure may besubstantially spherical. FIG. 2B illustrates an example in which thediameter of the microspheres ranges from about 900 μm to about 1200 μm.

FIG. 3 is an example scanning electron microscopy (SEM) image of anexterior of a microsphere formed in accordance with aspects of thisdisclosure. Prior to collection of the SEM image, the microsphere waslyophilized. Before lyophilization (freeze drying), saline was removedfrom the microsphere by rinsing the microsphere repeatedly withdeionized water. The resulting microsphere was frozen in liquidnitrogen, and lyophilized to remove any residual water from pores of themicrosphere. The SEM image was obtained utilizing a JEOL JSM-6700 SEM(available from JEOL USA, Inc., Peabody, Mass.). FIG. 3 was collected at55× magnification at 2.0 kilovolts (kV). The microsphere in FIG. 3 had adiameter of about 1100 μm.

FIGS. 4A and 4B are examples of SEM images of a hydrogel prepared withCCN crosslinked with CMC in accordance with aspects of the disclosure.The hydrogel was cut to expose an interior of the hydrogel and revealthe porous structure of the hydrogel. The SEM images were collectedusing a JEOL JSM-6700 SEM. FIG. 4A was collected at 500× magnification,while FIG. 4B was collected at 1000× magnification. Because the hydrogelwas prepared using CCN crosslinked with CMC, the internal structure ofmicrospheres formed in accordance with this disclosure is expected to besimilarly porous.

In some examples, in addition to being utilized as an embolizing agent,the microspheres may be used to deliver a therapeutic agent to a therapysite. The microspheres comprising CCN crosslinked with CMC may carrytherapeutic agent due to functional groups on the CCN crosslinked withCMC. For example, the microspheres may be loaded with a therapeuticagent, such as a chemotherapeutic agent, and used to deliver thechemotherapeutic agent to a tumor and/or to embolize arteries that feedthe tumor. In other embodiments, the microspheres may be loaded with acell, a bioactive molecule, or another drug.

An example of a therapeutic agent that may be loaded into themicrospheres is doxorubicin (available under the trade designationAdriamycin from Selleck Chemicals LLC, Houston, Tex., U.S.A.).Doxorubicin includes a protonated amino group and a plurality ofhydroxyl groups, which may interact with functional groups, such as acarboxylic group, in the microsphere to bind to the microsphere viaionic interactions. While doxorubicin is provided as one example of atherapeutic agent which may be loaded into the microspheres of thepresent disclosure, other therapeutic agents may be used with themicrospheres. For example, hydrophilic therapeutic agents may beutilized with the microspheres according to the disclosure. Inparticular, therapeutic agents that include at least one functionalgroup that interacts with a carboxylic group, hydroxyl group or analdehyde group are expected to be compatible with microspheres of thepresent disclosure. Examples of such therapeutic agents includeirinotecan (available under the trade designation Camptosar® fromPfizer, New York, N.Y., U.S.A), ambroxol, and other therapeutic agentswith at least one positively charged functional group. In someembodiments, in addition to ionic interactions between the therapeuticagent and the CCN crosslinked with CMC, the therapeutic agent may adsorbor adsorb in the microsphere.

In some embodiments, the therapeutic agent may be loaded into themicrospheres during formation of the microspheres, i.e., during thecrosslinking of the CCN with the partially oxidized CMC. In suchembodiments, the therapeutic agent may be deposited into the emulsionalong with the CCN and oxidized CMC. As the microspheres form, thetherapeutic agent may load into the microspheres.

In other embodiments, the therapeutic agent may be loaded into themicrospheres after formation of the microspheres. For example, themicrospheres may be immersed in a solution of the therapeutic agent in asolvent, such as saline or a saline and contrast medium mixture, to loadthe therapeutic agent into the microsphere. In some examples, thetherapeutic agent solution may have a concentration of between about 1mg therapeutic agent per mL solvent (mg/mL) and about 2 mg/mL.

In some examples, the therapeutic agent may be loaded into themicrospheres to a concentration of between about 0.3 mg therapeuticagent per mg dry microsphere (mg/mg) and about 0.75 mg/mg.

FIGS. 5A-5F are light microscopy images illustrating an example ofloading a dye (Evan's blue) into microspheres comprising CCN crosslinkedwith CMC. FIG. 5A illustrates a plurality of microspheres suspended innormal saline prior to the dye being loaded into the microspheres. Priorto introducing the Evan's blue, saline was removed to the extentpracticable using a micropipette, leaving wet microspheres. About 1 mLof a 1% w/v solution of Evan's blue in saline was added to about 50 mgwet microspheres. FIG. 5B was collected about 50 seconds afterintroducing the Evan's blue solution, and illustrates that loading ofthe dye into the microspheres has begun. FIG. 5C was taken about 4minutes after introduction of the Evan's blue solution, and shows thatadditional dye has been loaded into the microspheres. FIG. 5D wascollected about 16 minutes after introduction the Evan's blue solution,and shows further dye uptake by the microspheres. Finally, FIGS. 5E and5F illustrate microspheres loaded with the dye suspended in normalsaline after being removed from the Evan's blue solution.

FIGS. 6A-6C illustrate examples of microspheres according to an aspectof the disclosure after being loaded with various dyes. Specifically,FIG. 6A shows a plurality of microspheres loaded with seafoam green foodcoloring, FIG. 6B shows a plurality of microspheres loaded with FD&C RedDye #40, and FIG. 6C shows a plurality of microspheres loaded with FD&CYellow Dye #5. Prior to collecting the images shown in FIGS. 6A-6C, themicrospheres were loaded with the dye in a similar manner to thatdescribed above with respect to FIGS. 5A-5F: saline was removed from asuspension of microspheres in saline using a micropipette, and about 1mL of a 1% w/v solution of the dye in saline was added to about 50 mgwet microspheres. After loading the dye into the microspheres, theremaining dye solution was removed using a micropipette and thedye-loaded microspheres were suspended in saline. FIGS. 5A-5F and 6A-6Cillustrate that the microspheres may be loaded with dyes havingdifferent functional groups, suggesting that the microspheres may alsobe loaded with therapeutic agent that include different functionalgroups.

FIGS. 7A-7D are images taken with a light microscope illustrating anexample of loading doxorubicin into microspheres that include CCNcrosslinked with CMC. FIG. 7A illustrates a plurality of microspheressuspended in normal saline prior to the doxorubicin being loaded intothe microspheres. Prior to introducing the doxorubicin, saline wasremoved to the extent practicable using a micropipette, leaving wetmicrospheres. The doxorubicin solution was prepared by dissolving about50 microliters (μL) of a commercially available doxorubicin solution (2mg doxorubicin per mL solvent; available from Plantex USA, WoodcliffLake, N.J., U.S.A.) in about 200 μL saline. The resulting 250 μLsolution was added to about 20 mg wet microspheres. FIG. 7B wascollected about 45 seconds after introducing the doxorubicin solution,and illustrates that loading of the doxorubicin into the microsphereshas begun. FIG. 7C was taken about 10 minutes after introduction of thedoxorubicin solution, and shows that additional doxorubicin has beenloaded into the microspheres and the concentration of the doxorubicin inthe medium has decreased. FIG. 7D was collected about 30 minutes afterintroduction the doxorubicin solution, and shows further doxorubicinuptake by the microspheres and depletion of the doxorubicin from themedium. Finally, FIG. 8 illustrates microspheres loaded with thedoxorubicin suspended in a new solvent mixture (4:6, contrast:saline).

FIG. 9 is a scatter diagram illustrating examples of dynamics of loadingdoxorubicin into microspheres of various sizes. The loading ofdoxorubicin into the microspheres was performed in a saline medium. InFIG. 9 , the triangles represent loading of doxorubicin into a pluralityof microspheres having diameters of between about 300 μm and about 500μm, the squares represent loading of doxorubicin into a plurality ofmicrospheres having diameters between about 500 μm and about 700 μm, andthe diamonds represent loading of doxorubicin into a plurality ofmicrospheres having diameters between about 700 μm and about 850 μm. Theordinate represents the amount of doxorubicin in milligrams permilligram of dry microsphere. The abscissa represents loading time inminutes.

FIG. 10 is a scatter diagram illustrating examples of dynamics ofloading doxorubicin into microspheres of various sizes. The loading ofdoxorubicin into the microspheres was performed in a saline medium. InFIG. 10 , the downward-pointing triangles represent loading ofdoxorubicin into a plurality of microspheres having diameters of betweenabout 700 μm and about 850 μm, the upward-pointing triangles representloading of doxorubicin into a plurality of microspheres having diametersbetween about 500 μm and about 700 μm, the circles represent loading ofdoxorubicin into a plurality of microspheres having diameters betweenabout 300 μm and about 500 μm, and the squares represent loading ofdoxorubicin into a plurality of microspheres having diameters betweenabout 100 μm and about 300 μm. Similar to FIG. 9 , the ordinaterepresents the amount of doxorubicin in milligrams per milligram of drymicrosphere. The abscissa represents loading time in hours. Both FIG. 9and FIG. 10 show that in some embodiments a higher concentration ofdoxorubicin may be loaded into microspheres with smaller diameters. Forexample, doxorubicin may be loaded to a higher concentration inmicrospheres with diameters between about 100 μm and about 300 μm thatin microspheres with diameters between about 700 μm and about 850 μm.

FIG. 11 is a scatter diagram that illustrates examples of changes indiameter during loading of doxorubicin for microspheres of differentinitial diameters. As illustrated in FIG. 11 , the diameter of themicrospheres initially decreased during loading of doxorubicin andeventually reaches a substantially constant diameter. While not wishingto be bound by theory, this may be because the doxorubicin moleculesinclude positively-charged functional groups while the microspheres areformed of CCN crosslinked with CMC, and CCN and CMC includenegatively-charged functional groups. Thus, it is believed that in theabsence of the doxorubicin molecules, the negatively-charged functionalgroups on the CCN crosslinked with CMC may repulse each other. Thepresence of doxorubicin in the interior of the microsphere may bring thenet charge in the interior of the microsphere closer to zero, and thusmay reduce electrostatic repulsion in the microsphere, which may reducethe diameter of the microsphere.

In FIG. 11 , the squares represent a microsphere with an initialdiameter of about 280 μm, the circles represent a microsphere with aninitial diameter of about 490 μm, the diamonds represent a microspherewith an initial diameter of about 610 μm, and the triangles represent amicrosphere with an initial diameter of about 720 μm.

FIG. 12 is an example fluorescence microscopy image of a microsphereloaded with doxorubicin. FIG. 13 is an example image illustratingfluorescence intensity as a function of distance for a singledoxorubicin-loaded microsphere. Doxorubicin fluoresces under excitation.FIG. 13 illustrates substantially similar fluorescence across thesurface of the microsphere, which may suggest substantially similardoxorubicin loading across the surface of the microsphere. Themicrospheres illustrated in FIGS. 12 and 13 were formed of CCNcrosslinked with partially oxidized CMC.

FIG. 14 is a scatter diagram illustrating an example of a percentage ofdoxorubicin released as a function of time, measured in minutes, foreach of a plurality of samples of microspheres having differentcharacteristics. Each of the samples was disposed in about 2 mL salinefor the duration of the measurement. The saline was not changed duringthe measurement. The different samples of microspheres includeddifferent diameter ranges and different initial weights (total initialweight of microspheres loaded with doxorubicin). For example, four ofthe samples included microspheres with diameters between about 300 μmand about 500 μm. For a first of these samples, represented by thesmaller upward-pointing triangles, the plurality of microspheres had anaverage initial weight of about 5.3 mg; a second of these samples,represented by smaller squares, included a plurality of microsphereshaving an average initial weight of about 3.7 mg; a third of thesesamples, represented by the smaller diamonds, included a plurality ofmicrospheres having an average initial weight of about 3.6 mg; and afourth of these samples, represented by longer horizontal lines,included a plurality of microspheres having an average initial weight ofabout 3.3 mg.

Four additional samples included microspheres with diameters betweenabout 500 μm and about 700 μm. For a first of these samples, representedby shorter horizontal lines, the plurality of microspheres had anaverage initial weight of about 4.5 mg; a second of these samples,represented by crosses, included a plurality of microspheres having anaverage initial weight of about 4 mg; a third of these samples,represented by circles, included a plurality of microspheres having anaverage initial weight of about 3.5 mg; and a fourth of these samples,represented by asterisks, included a plurality of microspheres having anaverage initial weight of about 3.2 mg.

An additional four samples included microspheres with diameters betweenabout 700 μm and about 850 μm. For a first of these samples, representedby x's, the plurality of microspheres had an average initial weight ofabout 5 mg; a second of these samples, represented by the largerupward-pointing triangles, included a plurality of microspheres havingan average initial weight of about 4.9 mg; a third of these samples,represented by the larger squares, included a plurality of microsphereshaving an average initial weight of about 3.2 mg; and a fourth of thesesamples, represented by larger diamonds, included a plurality ofmicrospheres having an average initial weight of about 3 mg.

FIG. 15 is a scatter diagram illustrating examples of an amount ofdoxorubicin in milligrams released as a function of time, measured indays, for each of a plurality of samples of microspheres havingdifferent characteristics. Each of the samples was disposed in a cuvettefilled with about 2 mL saline. For some of the samples, the microsphereswere disposed in the same volume of saline for the duration of themeasurement. For other samples, the saline in which the microspheresloaded with doxorubicin were disposed was changed periodically. Inparticular, the saline was changed after 1 day, 3 days, 6 days, 12 days,19 days, and 26 days. Additionally, in the samples in which the salinewas changed periodically, the cuvette in which the microspheres andsaline were disposed was changed after 12 days and after 26 days.

The different samples of microspheres included different diameter rangesand different initial weights (of the microspheres loaded withdoxorubicin). For example, four of the samples included microsphereswith diameters between about 300 μm and about 500 μm. A first of thesesamples, represented by smaller upward-pointing triangles, included aplurality of microspheres having an average initial weight of about 4.8mg (the saline in which the first sample was disposed was changed asdescribed above). A second of these samples, represented by largersquares, included a plurality of microspheres having an average initialweight of about 4.3 mg (the saline in which the second sample wasdisposed was not changed). A third of these samples, represented bysmaller diamonds, included a plurality of microspheres having an averageinitial weight of about 3.3 mg (the saline in which the third sample wasdisposed was changed as described above). A fourth of these samples,represented by longer horizontal lines, included a plurality ofmicrospheres having an average initial weight of about 3.1 mg (thesaline in which the fourth sample was disposed was not changed).

Four more samples illustrated in FIG. 15 included microspheres withdiameters between about 500 μm and about 700 μm. A first of thesesamples, represented by shorter horizontal lines, included a pluralityof microspheres having an average initial weight of about 4.8 mg (thesaline in which the first sample was disposed was changed as describedabove). A second of these samples, represented by crosses, included aplurality of microspheres having an average initial weight of about 4.5mg (the saline in which the second sample was disposed was not changed).A third of these samples, represented by circles included a plurality ofmicrospheres having an average initial weight of about 3.7 mg (thesaline in which the third sample was disposed was changed as describedabove). A fourth of these samples, represented by asterisks, included aplurality of microspheres having an average initial weight of about 3.4mg (the saline in which the fourth sample was disposed was not changed).

An additional four samples shown in FIG. 15 included microspheres withdiameters between about 700 μm and about 850 μm. A first of thesesamples, represented by x's, included a plurality of microspheres havingan average initial weight of about 4.5 mg (the saline in which the firstsample was disposed was changed as described above). A second of thesesamples, represented by larger, upward-pointing triangles, included aplurality of microspheres having an average initial weight of about 4.2mg (the saline in which the second sample was disposed was not changed).A third of these samples, represented by smaller squares, included aplurality of microspheres having an average initial weight of about 4.0mg (the saline in which the third sample was disposed was changed asdescribed above). A fourth of these samples, represented by largerdiamonds, included a plurality of microspheres having an average initialweight of about 3.2 mg (the saline in which the fourth sample wasdisposed was not changed).

FIG. 16 is a scatter diagram illustrating examples of an amount ofdoxorubicin released in a saline medium as a function to time, measuredin days, for each of a plurality of samples of microspheres havingdifferent characteristics. Each of the samples was disposed in a cuvettefilled with 2 mL saline. For the first sample, the plurality ofmicrospheres had diameters between about 300 μm and about 500 μm and themicrospheres had an initial average initial weight of about 4.3 mg (theweight of the microspheres loaded with doxorubicin). The first sample,represented by squares, was disposed in the same saline for the durationof the measurement. For the second sample, represented by triangles, thesaline in which the microspheres loaded with doxorubicin were disposedwas changed periodically. In particular, the saline was changed after 1day, 3 days, 6 days, 12 days, 19 days, and 26 days. Additionally, thecuvette in which the second sample was disposed was changed after 12days and after 26 days. The second sample included microspheres with adiameter of between about 300 μm and about 500 μm and the microsphereshad an average initial weight of about 4.8 mg.

FIG. 17 is a scatter diagram illustrating examples of an amount ofdoxorubicin released in a saline medium as a function to time, measuredin days, for each of a plurality of samples of microspheres havingdifferent characteristics. Each of the samples was disposed in a cuvettefilled with 2 mL saline. For the first sample, represented by squares,the plurality of microspheres had a diameter between about 500 μm andabout 700 μm and was loaded with doxorubicin to an average initialweight of about 4.5 mg. The first sample was disposed in the same salinefor the duration of the measurement. For the second sample, the salinein which the microspheres loaded with doxorubicin were disposed waschanged periodically. In particular, the saline was changed after 1 day,3 days, 6 days, 12 days, 19 days, and 26 days. Additionally, the cuvettein which the second sample was disposed was changed after 12 days andafter 26 days. The second sample included microspheres with a diameterof between about 500 μm and about 700 μm and the microspheres wereloaded with doxorubicin to an average initial weight of about 4.8 mg.

FIG. 18 is a scatter diagram illustrating examples of an amount ofdoxorubicin released in a saline medium as a function to time, measuredin days, for each of a plurality of samples of microspheres havingdifferent characteristics. Each of the samples was disposed in a cuvettefilled with 2 mL saline. For the first sample, represented byupward-pointing triangles, the plurality of microspheres had a diameterbetween about 700 μm and about 850 μm and was loaded with doxorubicin toa total average initial weight of about 4.2 mg. The first sample wasdisposed in the same saline for the duration of the measurement. For thesecond sample, the saline in which the microspheres loaded withdoxorubicin were disposed was changed periodically. In particular, thesaline was changed after 1 day, 3 days, 6 days, 12 days, 19 days, and 26days. Additionally, the cuvette in which the second sample was disposedwas changed after 12 days and after 26 days. The second sample,represented by x's, included microspheres with a diameter of betweenabout 700 μm and about 850 μm and the microspheres were loaded to atotal average initial weight of about 4.5 mg.

FIG. 19 is a line diagram that illustrates an example comparison ofdoxorubicin release rate between microspheres of two different diameterranges. Each of the samples was placed in a cuvette filled with about 2mL normal saline and the concentration of the doxorubicin in the salinewas measured periodically. The saline in which the microspheres loadedwith doxorubicin were disposed was changed after 1 day, 3 days, 6 days,12 days, 19 days, and 26 days. Additionally, the cuvettes in which thesamples were disposed were changed after 12 days and after 26 days. Thefirst sample, represented by squares in FIG. 19 , included microsphereswith diameters between about 100 μm and about 300 μm. The initial weightof the 100 μm to 300 μm microspheres was about 4.4 mg. The secondsample, represented by open circles in FIG. 19 , included microsphereswith diameters between about 300 μm and about 500 μm. The initial weightof the 300 μm to 500 μm microspheres was about 4.8 mg. FIG. 19 showsthat in this example, the larger microspheres initially release thedoxorubicin somewhat slower than the smaller microspheres, but thelarger microspheres provided a somewhat more sustained release of thedoxorubicin (e.g., after about 20 days).

FIG. 20 is a line diagram that illustrates examples of release ofdoxorubicin from microspheres in different media. The data pointsillustrated as squares in FIG. 20 represent release of doxorubicin frommicrospheres placed in normal saline, which had a pH of between about5.5 and 6.0. The data points illustrated as circles in FIG. 20 representrelease of doxorubicin from microspheres placed in acetate bufferedsaline, which had a pH of about 5.2. The data points illustrated astriangles in FIG. 20 represent release of doxorubicin from microspheresplaced in PBS, which had a pH of about 7.4. The medium was not changedfor any of the samples during the duration of the testing.

In each of the samples, the diameters of the microspheres were betweenabout 300 μm and about 500 μm. Each of the microspheres was initiallyloaded with about 0.22 mg doxorubicin. In FIG. 20 , the concentration ofdoxorubicin in the medium, measured in mg doxorubicin per mL medium, isplotted as a function of time, measured in days.

FIG. 20 shows that in this example, a greater amount of doxorubicin wasgenerally released from the microspheres when the surrounding medium hada lower pH. For example, the microspheres in the PBS medium, which hadthe highest pH, released doxorubicin to a concentration in the medium ofless than about 0.025 mg/mL. In the acetate buffered saline and thenormal saline, doxorubicin was released from the microspheres to aconcentration in the medium of about 0.045 mg/mL.

As described above, the degree of oxidation of the CMC may be controlledin the initial oxidizing reaction when preparing partially oxidized CMC.The degree of oxidation may be defines as the number of repeating unitsoxidized per 100 repeating units. As described above, CMC with a higherdegree of oxidation may result in more crosslinks when reacted with CCN.FIG. 21 is a line diagram that illustrates an example of the effect thedegree of oxidation of the CMC may have on the release rate ofdoxorubicin from microspheres that are formed of CCN crosslinked withCMC. In FIG. 21 , the concentration of doxorubicin in the medium,measured in mg doxorubicin per mL medium, is plotted as a function oftime, measured in days. The microspheres in each sample had diametersbetween about 300 μm and about 500 μm, and each sample of themicrospheres was initially loaded with an average of about 0.50 mgdoxorubicin.

The data points illustrated in FIG. 21 by squares represent thedoxorubicin released from microspheres formed of CCN crosslinked withCMC with a degree of oxidation of about 10% (i.e., about 1 in 10repeating units of the CMC was oxidized). The data points illustrated inFIG. 21 by circles represent the doxorubicin release from microspheresformed of CCN crosslinked with CMC with a degree of oxidation of about25%. The data points illustrated in FIG. 21 by triangles represent thedoxorubicin release from microspheres formed of CCN crosslinked with CMCwith a degree of oxidation of about 50%. Thus, FIG. 21 illustrates thatin this example, a greater amount of doxorubicin was released from themicrospheres formed of CCN crosslinked with CMC with a lower degree ofoxidation (correlating with a lower crosslinking density).

FIG. 22 is a line diagram that illustrates an example of the effect ofthe medium on the release of doxorubicin from microspheres formed of CCNcrosslinked with CMC. In FIG. 22 , the concentration of doxorubicin inthe medium, measured in mg doxorubicin per mL medium, is plotted as afunction of time, measured in days. The microspheres were formed of CCNcrosslinked with CMC, and had diameters between about 300 μm and about500 μm. The average initial weight of the microspheres was about 3.1 mg(including doxorubicin), and about 0.18 mg of the weight wasdoxorubicin. As shown in FIG. 22 , the microspheres were initiallyplaced in a water medium, and little doxorubicin was released from themicrospheres formed of CCN crosslinked with CMC. However, after abouttwo and one half days, the microspheres were placed in a saline medium,and doxorubicin began being released from the microspheres in greateramounts. This may suggest that ion exchange plays a role in the releaseof doxorubicin from the microspheres formed of CCN crosslinked with CMC.

FIG. 23 is a line diagram that illustrates an example comparison betweenrelease rates of doxorubicin from microspheres according to an aspectthe disclosure and DC Beads™, a polyvinyl alcohol-based embolizationbead available from Biocompatibles, Farnham, Surrey, United Kingdom. Themicrospheres formed of CCN crosslinked with CMC had diameters betweenabout 300 μm and about 500 μm, and initial doxorubicin loading was about0.50 mg. The DC Beads™ also had diameters between about 300 μm and about500 μm, and were loaded with an average of about 0.50 mg doxorubicin.Each of the samples was placed in PBS for the duration of the testing.In FIG. 23 , the concentration of doxorubicin in the PBS, measured in mgdoxorubicin per mL PBS, is plotted as a function of time, measured inhours. In this example, the release of doxorubicin from the CCNcrosslinked with CMC microspheres may be more gradual and sustained thanthe release of doxorubicin from the DC Beads™ microspheres.

In some embodiments, regardless of whether the microspheres are loadedwith drug, the microspheres comprising CCN crosslinked with CMC may haveadvantageous mechanical properties. For example, the microspheres may becompressible, and may substantially return to their original shape afterbeing compressed. FIG. 24 is a plot of compression force versus distancefor a single microsphere having a diameter of about 715 μm and acrosslinking density of about 10%. The compression test was performedusing a TA.XTPlus Texture Analyzer (Texture Technologies Corp.,Scarsdale, N.Y.). The microsphere was compressed at a rate of about 0.08mm/s. As illustrated in FIG. 24 , the microsphere compresses about 622μm (0.622 mm) before irreversibly deforming, resulting in a fracturestrain of about 87%. Additionally, the compression force at fracture wasabout 65.5 g. As described above, the fracture strain may be adjustedbetween about 70% and about 90% by controlling a crosslinking densitybetween the CCN and CMC.

FIGS. 25A-25C are light microscopy images illustrating an example of thecompressibility of a microsphere comprising CCN crosslinked with CMC asthe microsphere passes through a polyethylene tube. The microsphere hasa diameter of about 925 μm and the catheter has an internal diameter ofabout 580 μm (PE-50). As FIGS. 25B and 25C illustrate, the microspherecan deform and pass through the internal cavity of the catheter.

FIGS. 26A-26C are light microscopy images that illustrate anotherexample of the compressibility of a microsphere comprising CCNcrosslinked with CMC and having a diameter of about 860 μm as themicrosphere passes through a polyethylene tube. In FIGS. 26A-26C, thecatheter again has an internal diameter of about 580 μm (PE-50). AsFIGS. 26B and 26C illustrate, the microsphere can reversibly deform,pass through the internal cavity of the catheter, and return to a shapeand size substantially similar to the shape and size of the microspherebefore passing through the catheter.

FIGS. 27A and 27B illustrate an example of the resiliency of amicrosphere comprising CCN crosslinked with CMC. The microspherepictured in FIGS. 27A and 27B has a diameter of about 675 μm and wasdisposed in a polyethylene tube with an internal diameter of about 580μm (PE-50) for about 24 hours prior to being released. The image shownin FIG. 27A was collected about 3 seconds after the microsphere wasreleased from the PE tube, and the image shown in FIG. 27B was collectedabout 5 seconds after the microsphere was released. FIGS. 27A and 27Billustrate that the microsphere may recover its spherical shape andoriginal size relatively quickly after being released from the PE tube.

FIG. 28 is a light microscopy image of an example of microspheres havingdiameters between about 500 μm and about 700 μm taken after themicrospheres were injected through a catheter with an internal diameterof about 480 μm (2 French catheter, available from Boston ScientificCorp., Natick, Mass.). As illustrated in FIG. 28 , the microspheressubstantially retained their original, spherical shape.

FIGS. 29A and 29B are light microscopy images of an example ofmicrospheres having diameters between about 800 μm and about 1000 μmtaken after the microspheres were injected through a catheter with aninternal diameter of about 0.53 mm (3 French catheter, Terumo MedicalCorp., Somerset, N.J.). As illustrated in FIGS. 29A and 29B, themicrospheres substantially retained their original, spherical shape.

FIGS. 30A and 30B are light microscopy images of an example ofmicrospheres loaded with doxorubicin while passing through a catheterand after passing through the catheter. The microspheres illustrated inFIGS. 30A and 30B have a diameter between about 500 μm and about 700 μm.The catheter shown in FIG. 30A had an internal diameter of about 0.53 mm(3 French catheter, Terumo Medical Corp., Somerset, N.J.). As shown inFIG. 30B, the microspheres substantially retained their original,spherical shape.

FIGS. 31A and 31B are light microscopy images of an example ofmicrospheres loaded with doxorubicin while passing through apolyethylene tube. The microspheres illustrated in FIGS. 31A and 31Bhave a diameter between about 500 μm and about 700 μm. The cathetershown in FIGS. 31A and 31B had an internal diameter of about 580 μm(PE-50).

Microspheres according to the present invention may be suspended in avariety of solvents. For example, FIGS. 32A and 32B are imagesillustrating microspheres comprising CCN crosslinked with CMC suspendedin two different mixtures. In FIG. 32A, the microspheres are suspendedin a mixture of 40% contrast medium and 60% saline. As FIG. 32Aillustrates, the microspheres are suspended in the mixture, and aretranslucent. FIG. 32B illustrates microspheres dyed with Evan's bluesuspended in a 50% contrast medium and 50% saline mixture.

Microspheres comprising CNN crosslinked with CMC may be somewhat stablewhen stored in water, but eventually may begin to degrade. FIG. 33 is alight microscopy image of an example of a plurality of microspheresafter being stored for two months in water. The microspheres shown inFIG. 33 had a crosslinking density of about 10%. The microspheres shownin FIG. 33 have been dyed with Evan's blue to increase contrast with thebackground medium (water). As FIG. 33 illustrates, the microspheres havebegun to degrade and show decreased mechanical integrity.

In some examples, microspheres comprising CCN crosslinked with CMC maydegrade more rapidly in the presence of an enzyme such as lysozyme.FIGS. 34A-34E are light microscopy images that illustrate an example ofa plurality of microspheres degrading in the presence of lysozyme. Themicrospheres had a crosslinking density of about 10%. The mediumsurrounding the microspheres contained 4 mg/mL lysozyme and themicrospheres and surrounding medium were kept at a temperature of about37° C. for the duration of the test. FIG. 34A illustrates the appearanceof the microspheres on day 0, soon after the microspheres were placed inthe medium. FIG. 34B shows the appearance of the microspheres on day 3.FIG. 34C illustrates the appearance of a microsphere after 7 days.Visual evidence of the beginning of degradation is apparent. FIG. 34Dshows the appearance of a microsphere on day 9. Degradation of themicrosphere is progressing, mechanical integrity is decreasing, and themicrosphere is no longer spherical. Finally, FIG. 34E illustrates theappearance of a microsphere on day 14, at which time pieces ofmicrosphere can be found in the medium, but the microsphere is no longerspherical.

As described above, the degradation time of the microspheres may beadjusted by increasing or decreasing the crosslink density in themicrospheres. For example, a higher crosslink density, which maycorrespond to a higher oxidation degree of the partially oxidized CMC,may lead to an increased degradation time, while a lower crosslinkdensity (a lower oxidation degree of the CMC) may lead to a decreaseddegradation time.

FIGS. 35A-35C are light microscopy images that illustrate anotherexample of a plurality of microspheres loaded with doxorubicin degradingin the presence of lysozyme. The microspheres were prepared from OCMC-II(preparation described in Example 1 below) and CCN-III (preparationdescribed in Example 6 below) and had diameters ranging from about 500μm to about 700 μm. The microspheres were placed in a 2 mg/mL solutionof doxorubicin in saline for about 24 hours to load the microsphereswith doxorubicin. The medium surrounding the microspheres contained 4mg/mL lysozyme in PBS and the microspheres and PBS were kept at atemperature of about 37° C. for the duration of the test. FIG. 35Aillustrates the appearance of the microspheres on day 0, soon after themicrospheres were placed in the PBS. FIG. 35B shows the appearance ofthe microspheres after about 1.5 months. FIG. 35C illustrates theappearance of a microsphere after about 3 months. Visual evidence of thebeginning of degradation is apparent in FIG. 35C.

FIGS. 36A and 36B are light microscopy images illustrating an example ofmicrospheres comprising CCN crosslinked with CMC 32 cultured with humandermal fibroblasts 34. The human dermal fibroblasts 34 show no apparentadverse effects due to the presence of micro spheres 32.

FIGS. 37A and 37B are light microscopy images of an example controlincluding cultured human fibroblast and an example of a sample includinghuman dermal fibroblast cultured with microspheres comprising CCNcrosslinked with CMC, respectively. The control and sample have beenstained with crystal violet. Again, the human dermal fibroblast shows noapparent adverse effects due to the presence of microspheres.

FIG. 38A-38C are light microscopy images illustrating an example of acontrol that included human dermal fibroblasts stained with crystalviolet. FIG. 38A is an image collected about 3 days after beginning ofthe fibroblast culture. FIG. 38B is an image collected about 7 daysafter beginning of the fibroblast culture. FIG. 38C is an imagecollected about 15 days after beginning of the fibroblast culture.

FIGS. 39A-39C are light microscopy images illustrating an example of asample including human dermal fibroblast cultured with microspherescomprising CCN crosslinked with CMC. The microspheres were prepared fromOCMC-I (preparation described in Example 1 below) and CCN-II(preparation described in Example 5 below). The cells were stained withcrystal violet. FIG. 39A is an image collected about 3 days afterbeginning of the culture. FIG. 39B is an image collected about 7 daysafter beginning of the culture. FIG. 39C is an image collected about 15days after beginning of the culture. Compared with the control shown inFIGS. 38A-38C, the human dermal fibroblast in FIGS. 39A-39C shows noapparent adverse effects due to the presence of microspheres.

FIG. 40 is a bar graph that illustrates an example of absorbance at awavelength of about 490 nm of medium cultured with human dermalfibroblasts after being treated with MTS(3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium,inner salt). MTS is a cell titer for live cells, and thus the absorbanceis proportional to the number of live cells in the culture. The controlincluded only human dermal fibroblast, while batch 1 and batch 2included human dermal fibroblast cultured with microspheres formed ofCCN crosslinked with CMC. Microspheres in batch 1 were prepared fromOCMC-I (preparation described in Example 1 below) and CCN-I (preparationdescribed in Example 4 below). Microspheres in batch 2 were preparedfrom OCMC-II and CCN-I (preparation described in Example 5 below). FIG.40 shows that in this example, there was no significant difference incell growth over the course of six days between the control, batch 1,and batch 2.

FIG. 41 is a bar graph that illustrates an example of the arterialdistribution of the microspheres after embolization of three pairs ofrabbit kidneys with microspheres having diameters between about 100 μmand about 300 μm. For comparative purposes, microspheres available underthe trade designation Embosphere® (available from BioSphere Medical,Inc., Rockland, Mass., U.S.A.) having diameters between about 100 μm andabout 300 μm were used. In each example, microspheres were injected intothe renal artery of live rabbits. The rabbits were then euthanized andthe kidneys removed to assess the results of the embolization. Thenumbers of microspheres for each of the Embosphere® microspheres and themicrospheres formed of CCN crosslinked with CMC were counted at a firstlocation in the interlobar artery (proximal to the injection site), thearcuate artery (median), and at a second location in the interlobarartery (distal to the injection site). The results are shown in FIG. 41as a percentage of the microspheres counted at each location.

FIG. 42 is bar diagram that illustrates an example comparison betweenEmbospheres® and microspheres formed of CCN crosslinked with CMC of themean diameter of the vessel occluded during an embolization procedure.In some examples, it may be desirable that the microspheres occludearteries with a certain, predetermined diameter. Accordingly, it may bedesirable to understand the relationship between a size range of themicrospheres and the average diameter occluded by the microspheres. Asin FIG. 41 , the nominal diameter of the Embospheres® used in theexample shown in FIG. 42 was between 100 μm and 300 μm. Similarly, thenominal diameter of the microspheres formed of CCN crosslinked with CMCwas between 100 μm and 300 μm. The mean diameter occluded by theEmbospheres® was about 150 μm, while the mean diameter occluded by themicrospheres formed of CCN crosslinked with CMC was about 200 μm.

FIG. 43 is a bar diagram that illustrates an example determination ofthe mean diameter of the microspheres formed of CCN crosslinked with CMCthat were used in the embolization procedure that generated the resultsshown in FIG. 42 . The bar labeled “CMC/CN microspheres” shows the meandiameter of the microspheres formed of CCN crosslinked with CMC asdetermined by optical micrography. The bar labeled “Sieve aperture”shows the calibrated mean diameter of the microspheres formed of CCNcrosslinked with CMC, determined by passing sieves with differentapertures and averaging the aperture sizes of the two adjacent sievesaperture, one of which the microspheres did not pass through and one ofwhich the microspheres did pass through. In this way, the sieve aperturemean diameter may be considered the mean diameter of compressedmicrospheres formed of CCN crosslinked with CMC. As shown in FIGS. 42and 43 , the sieve aperture mean diameter is substantially the same asthe mean diameter of the vessel occluded by the microspheres formed ofCCN crosslinked with CMC. This suggests that determining a sieveaperture mean diameter for microspheres formed of CCN crosslinked withCMC may predict a mean diameter of a vessel that may be occluded by themicrospheres.

FIGS. 44 and 45 are example histology sections of kidney tissue showingarcuate artery in a kidney of a rabbit occluded with an embolicmicrosphere 36 according to aspects of the disclosure. As shown in FIGS.44 and 45 , the embolic microsphere 36 occludes substantially all of theartery. The small interval between the embolic microsphere 36 and thewall of the vessel is believed to be caused by sample processing as themicrosphere 36 shrinks upon fixation.

Microspheres formed according to the present disclosure may be utilizedfor a number of applications. For example, one application for anembolic microsphere comprising CCN crosslinked by CMC is transareterialchemoembolization (TACE) of liver tumors. TACE for unresectablehepatocellular carcinoma (HCC) is an approved treatment modality thatincreases patient survival compared to intravenous chemotherapy. TACEincludes intraarterial (via the hepatic artery) injection ofchemotherapeutic agents followed by embolization of tumoral feedingarteries. The trend in TACE is to use drug eluting beads loaded withchemotherapeutic agents that are progressively released into the tumor.Drug eluting TACE is associated with less systemic toxicity and a betterpatient tolerance. Because the microsphere comprising CCN crosslinked byCMC is bioresorbable and is thus absorbed by the body of the patientover time after injection, the release profile of the chemotherapeuticagents may be controlled. Additionally, the microsphere comprising CCNcrosslinked by CMC may act as combination chemotherapeutic agentcarriers and embolization agents. Furthermore, because the microspherecomprising CCN crosslinked by CMC are bioresorbable, artery integritymay be restored upon resorption, which may be advantageous in someexamples.

Another application for microspheres comprising CCN crosslinked by CMCis Uterine Fibroids Embolization (UFE). Uterine Fibroids are benignmuscular tumors that grow in the wall of the uterus. Uterine fibroidscan grow as a single tumor or as many tumors. Uterine fibroids can beeither as small as an apple seed or as big as a grapefruit. In unusualcases uterine fibroids can become very large. An increasingly acceptedtherapy technique for uterine fibroids is UFE. The main purpose of UFEis to reduce the size of the fibroid and to treat excessive uterinebleeding. In essence, UFE involves the placement of a catheter into theuterine arteries and injection of embolization microspheres into theuterine arteries to achieve fibroid devascularization and progressiveshrinkage. Use of bioresorbable microspheres comprising CCN crosslinkedby CMC may facilitate restoration of uterine artery integrity afterembolization.

EXAMPLES Example 1: Preparation of Partially Oxidized CMC

About 1 g of sodium carboxymethyl cellulose (Sigma-Aldrich, St. Louis,Mo., M_(w) about 700,000 g/mol) and 80 mL distilled water were added toa 250 mL flask. After the carboxymethyl cellulose dissolvedsubstantially completely, 25% molar equivalent of sodium periodate in 20mL distilled water was added to the flask. The reaction was allowed toproceed for 24 hours at about 25° C. After 24 hours, about 0.21 gethylene glycol was added to the flask to stop the reaction. After anadditional 30 minutes, the mixture was poured into a dialysis tube (MWCO3500) to dialyze against distilled water for 3 days. Dry product wasobtained by lyophilizing the dialyzed solution. The resulting partiallyoxidized CMC was labeled OCMC-II.

Example 2: Preparation of Partially Oxidized CMC

About 1 g of sodium carboxymethyl cellulose (Sigma-Aldrich, St. Louis,Mo., M_(w) about 700,000 g/mol) and 80 mL distilled water were added toa 250 mL flask. After the carboxymethyl cellulose dissolvedsubstantially completely, 10% molar equivalent of sodium periodate in 20mL distilled water was added to the flask. The reaction was allowed toproceed for 24 hours at about 25° C. After 24 hours, about 0.08 gethylene glycol was added to the flask to stop the reaction. After anadditional 30 minutes, the mixture was poured into a dialysis tube (MWCO3500) to dialyze against distilled water for 3 days. Dry product wasobtained by lyophilizing the dialyzed solution. The resulting partiallyoxidized CMC was labeled OCMC-I.

Example 3: Preparation of Partially Oxidized CMC

About 1 g of sodium carboxymethyl cellulose (Sigma-Aldrich, St. Louis,Mo., M_(w) about 700,000 g/mol) and 80 mL distilled water were added toa 250 mL flask. After the carboxymethyl cellulose dissolvedsubstantially completely, 50% molar equivalent of sodium periodate in 20mL distilled water was added to the flask. The reaction was allowed toproceed for 24 hours at about 25° C. After 24 hours, about 0.42 gethylene glycol was added to the flask to stop the reaction. After anadditional 30 minutes, the mixture was poured into a dialysis tube (MWCO3500) to dialyze against distilled water for 3 days. Dry product wasobtained by lyophilizing the dialyzed solution. The resulting partiallyoxidized CMC was labeled OCMC-III.

Example 4: Preparation of CCN

In a 3-neck flask, about 2 g chitosan (Sigma-Aldrich, St. Louis, Mo.,greater than 75% deacetylated) was added to a mixture of about 16 gsodium hydroxide, about 20 mL distilled water, and about 20 mLisopropanol. The mixture was stirred at about 25° C. for about 24 hours.Before carboxymethylation, the flask was maintained in a water bath atabout 50° C. for about 1 hour. About 16 g monochloroacetic acid(Sigma-Aldrich, St. Louis, Mo.) in 10 mL isopropanol then was addeddropwise into the reaction mixture. The reaction mixture was stirred atabout 50° C. for an additional 4 hrs, and the reaction was stopped byadding about 80 mL of 70% ethanol. The precipitate was filtered andrinsed thoroughly with 70-90% ethanol and vacuum dried at roomtemperature.

The dried product was dissolved in about 100 mL water and homogenizedfor 2 hours. Any insoluble residue present in the mixture was removed bycentrifuging. The supernatant was dialyzed in an MWCO 3500 dialysis tubeagainst distilled water and then lyophilized. The resulting CCN waslabeled CCN-I.

Example 5: Preparation of CCN

In a 3-neck flask, about 2 g chitosan (Sigma-Aldrich, St. Louis, Mo.,greater than 75% deacetylated) was added to a mixture of about 8 gsodium hydroxide, about 10 mL distilled water, and about 10 mLisopropanol. The mixture was stirred at room temperature for about 24hours. Before carboxymethylation, the flask was maintained in a waterbath at about 50° C. for about 1 hour. About 8 g monochloroacetic acid(Sigma-Aldrich, St. Louis, Mo.) in 5 mL isopropanol then was addeddropwise into the reaction mixture. The reaction mixture was stirred atabout 50° C. for an additional 4 hrs, and the reaction was stopped byadding about 80 mL of 70% ethanol. The precipitate was filtered andrinsed thoroughly with 70-90% ethanol and vacuum dried at roomtemperature.

The dried product was dissolved in about 100 mL water and homogenizedfor 2 hours. Any insoluble residue present in the mixture was removed bycentrifuging. The supernatant was dialyzed in an MWCO 3500 dialysis tubeagainst distilled water and then lyophilized. The resulting CCN waslabeled CCN-II.

Example 6: Preparation of CCN

In a 3-neck flask, about 2 g chitosan (Sigma-Aldrich, St. Louis, Mo.,greater than 75% deacetylated) was added to a mixture of about 8 gsodium hydroxide, about 8 mL distilled water, and about 32 mLisopropanol. The mixture was stirred for about 24 hours at about 25° C.Before carboxymethylation, the flask was maintained in a water bath atabout 50° C. for about 1 hour. About 16 g monochloroacetic acid(Sigma-Aldrich, St. Louis, Mo.) in 10 mL isopropanol then was addeddropwise into the reaction mixture. The reaction mixture was stirred atabout 50° C. for an additional 4 hrs, and the reaction was stopped byadding about 80 mL of 70% ethanol. The precipitate was filtered andrinsed thoroughly with 70-90% ethanol and vacuum dried at roomtemperature.

The dried product was dissolved in about 100 mL water and homogenizedfor 2 hours. Any insoluble residue present in the mixture was removed bycentrifuging. The supernatant was dialyzed in an MWCO 3500 dialysis tubeagainst distilled water and then lyophilized. The resulting CCN waslabeled CCN-III.

Example 7: Preparation of CCN and CMC Microspheres

About 0.075 g of CCN-I was mixed in about 5 mL of water to form a 1.5%w/v CCN-I solution. Similarly, about 0.075 g OCMC-I was mixed in about 5ml water to form a 1.5% w/v OCMC-I solution. The CCN-I and OCMC-Isolutions were then mixed. The mixture was added to about 50 mL mineraloil containing between 0.2 mL and 0.5 mL sorbitane monooleate to form anemulsion. The emulsion was homogenized for about 45 minutes. The aqueousphase of the emulsion was allowed to evaporate over night at about 45°C. with constant stirring. The crosslinked CCN and CMC was isolated byprecipitation in isopropanol followed by centrifugation to remove theoil phase. The resulting microspheres were washed thoroughly in acetonebefore being dried under vacuum. The mean diameter of the microspheres,measured in normal saline by a light microscope, was about 515±3 μm.

Example 8: Preparation of CCN and CMC Microspheres

About 0.075 g of CCN-I was mixed in about 5 mL of water to form a 1.5%w/v CCN-I solution. Similarly, about 0.075 g OCMC-II was mixed in about5 ml water to form a 1.5% w/v OCMC-I solution. The CCN-I and OCMC-IIsolutions were then mixed. The mixture was added to about 50 mL mineraloil containing between 0.2 mL and 0.5 mL sorbitane monooleate to form anemulsion. The emulsion was homogenized for about 45 minutes. The aqueousphase of the emulsion was allowed to evaporate over night at about 45°C. with constant stirring. The crosslinked CCN and CMC was isolated byprecipitation in isopropanol followed by centrifugation to remove theoil phase. The resulting microspheres were washed thoroughly in acetonebefore being dried under vacuum. The mean diameter of the microspheres,measured in normal saline by a light microscope, was about 594±3 μm.

Example 9: Preparation of CCN and CMC Microspheres

About 0.075 g of CCN-I was mixed in about 5 mL of water to form a 1.5%w/v CCN-I solution. Similarly, about 0.075 g OCMC-III was mixed in about5 ml water to form a 1.5% w/v OCMC-I solution. The CCN-I and OCMC-IIIsolutions were then mixed. The mixture was added to about 50 mL mineraloil containing between 0.2 mL and 0.5 mL sorbitane monooleate to form anemulsion. The emulsion was homogenized for about 45 minutes. The aqueousphase of the emulsion was allowed to evaporate over night at about 45°C. with constant stirring. The crosslinked CCN and CMC was isolated byprecipitation in isopropanol followed by centrifugation to remove theoil phase. The resulting microspheres were washed thoroughly in acetonebefore being dried under vacuum. The mean diameter of the microspheres,measured in normal saline by a light microscope was about 702±3 μm.

Example 10: Preparation of CCN and CMC Microspheres

About 0.1 g of CCN-II was mixed in about 5 mL of water to form a 2% w/vCCN-I solution. Similarly, about 0.1 g OCMC-II or 0.1 OCMC-III was mixedin about 5 ml water to form a 2% w/v OCMC-II solution or a 2% w/vOCMC-III solution. The CCN-I and OCMC-I solutions were then mixed. Themixture was added to about 50 mL mineral oil containing between 0.2 mLand 0.5 mL sorbitane monooleate to form an emulsion. The emulsion washomogenized for about 45 minutes. The aqueous phase of the emulsion wasallowed to evaporate over night at about 45° C. with constant stirring.The crosslinked CCN and CMC was isolated by precipitation in isopropanolfollowed by centrifugation to remove the oil phase. The resultingmicrospheres were washed thoroughly in acetone before being dried undervacuum. The mean diameter of the microspheres, measured in normal salineby a light microscope was about 2000 μm.

Example 11: Preparation of Doxorubicin-Loaded Microspheres

Microspheres disposed in saline and having wet weight of about 150 mgwere added into a 22 mL glass vial. (The microspheres had a dry weightof about 17 mg and were formed from OCMC-II and CCN-III.) Excess salinewas removed with a pipette. About 20 mL doxorubicin solution (about 2 mgdoxorubicin/mL solution) was formed by dissolving doxorubicin in asaline/hydrochloric acid solution having a pH between about 2.5 andabout 4.5 and was added into the vial. An amount of doxorubicinremaining in the loading solution after loading of the microspheres wasdetermined by measuring the absorbance at 482 nm using a BeckmanUV-Visible spectrophotometer and comparison to a standard curveconstructed from solutions of known concentrations of drug. The maximumloading is between about 0.3 and about 0.7 mg doxorubicin per mg drymicrospheres, depending on the size of the microspheres.

Example 12: Release of Doxorubicin in Saline

About 3 mg of loaded microspheres and about 2 mL normal saline wereadded into a disposable plastic cuvette. The concentration ofdoxorubicin released in the medium was monitored with a BeckmanUV-Visible spectrophotometer. The release of the doxorubicin wasaccomplished both with replacing normal saline at periodic intervals (onday 1, day 3, day 6, day 12, day 19, and day 26) and without replacingthe normal saline. The saline was saturated with doxorubicin in about 2weeks when the normal saline was not replaced. The release ofdoxorubicin when replacing the normal saline can last 1 month withoutsaturating the normal saline.

Various embodiments of the disclosure have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. A microsphere comprising carboxymethyl chitosancrosslinked with carboxymethyl cellulose and a therapeutic agent.
 2. Themicrosphere of claim 1, wherein the therapeutic agent comprises achemotherapeutic agent.
 3. The microsphere of claim 1, wherein thetherapeutic agent comprises at least one positively charged functionalgroup.
 4. The microsphere of claim 1, wherein the therapeutic agentcomprises at least one of irinotecan, ambroxol, or doxorubicin.
 5. Themicrosphere of claim 1, wherein a concentration of the therapeutic agentis between about 0.3 milligram of therapeutic agent per milligram of drymicrosphere and about 0.75 milligram of therapeutic agent per milligramof dry microsphere.
 6. The microsphere of claim 1, wherein themicrosphere is substantially free of a small molecule crosslinkingagent.
 7. The microsphere of claim 1, wherein the microsphere iscompressible.
 8. The microsphere of claim 1, further comprising acrosslinking density between the carboxymethyl chitosan and thecarboxymethyl cellulose that results in a fracture strain of the atleast one microsphere between about 70% and about 90%, and furtherdefining a diameter between about 50 micrometers and about 1200micrometers.
 9. The microsphere of claim 1, further comprising acrosslinking density between the carboxymethyl chitosan and thecarboxymethyl cellulose that results in a fracture strain of the atleast one microsphere between about 70% and about 90%, and furtherdefining a diameter between about 1600 micrometers and about 2200micrometers.
 10. A microsphere comprising carboxymethyl chitosancrosslinked with carboxymethyl cellulose, wherein the microsphere has acompressibility sufficient to permit the microsphere to be introducedthrough a catheter or syringe.
 11. The microsphere of claim 10, whereinthe microsphere comprises a diameter between about 50 micrometers andabout 1200 micrometers.
 12. The microsphere of claim 10, wherein themicrosphere comprises a diameter of between about 1600 micrometers andabout 2200 micrometers.
 13. The microsphere of claim 10, wherein themicrosphere further comprises a chemotherapeutic agent.
 14. Themicrosphere of claim 10, wherein the microsphere further comprises atleast one of irinotecan, ambroxol, or doxorubicin.
 15. The microsphereof claim 13, wherein a concentration of the chemotherapeutic agent isbetween about 0.3 milligram of therapeutic agent per milligram of drymicrosphere and about 0.75 milligram of therapeutic agent per milligramof dry microsphere.
 16. The microsphere of claim 10, wherein themicrosphere is substantially free of a small molecule crosslinkingagent.